Welding cast iron with a nickel copper electrode such as ENiCu-B is one of the most reliable repair techniques when performed correctly. Follow the steps below to minimize cracking and produce machinable, high-quality repair welds.
Step 1 - Assess and Prepare the Defect
Grind out cracks and defects until you reach clean, sound metal. Use a U-groove rather than a sharp V-groove to reduce stress concentration. Remove all oil, grease, and graphite smear.
Step 2 - Choose the Right Electrode
For most gray and ductile iron repairs, ENiCu-B (AWS A5.15) offers a good balance of ductility, machinability, and cost. Where color match or lower dilution is critical, ENi-CI or ENiFe-CI may be alternative choices.
Step 3 - Control Heat Input (Cold Welding Technique)
Cast iron is very sensitive to thermal shock. Use short stringer beads (25–40 mm) and let each bead cool almost to hand temperature before starting the next. This "cold welding" approach dramatically reduces the risk of HAZ cracking.
Step 4 - Peen Each Bead
Immediately after each bead, peen the weld with a rounded chipping hammer while it is still hot. Peening plastically deforms the weld metal and relieves shrinkage stress in the surrounding cast iron.
Step 5 - Recommended Parameters
For a 3.2 mm ENiCu-B electrode, start at 90–130 A DCEP and adjust to the smallest current that gives stable arc and full fusion. Excess current means excess dilution, which reduces the nickel content in the fusion zone and increases the risk of cracking.
Step 6 - Cool Slowly
After the last bead, insulate the part with ceramic wool or dry sand and let it cool slowly to room temperature. Rapid cooling is the number one cause of post-weld cracking in cast iron repair.
Common Defects and Fixes
- Porosity → clean base metal more thoroughly and redry electrodes
- HAZ cracks → reduce heat input, use shorter beads, peen every bead
- Weld cracks → check dilution; keep current low; consider preheating for large parts
Executed correctly, ENiCu-B produces welds that machine like mild steel and hold up under service loads that would fail brittle repairs.
